Often very precisely located operations must be performed on preforms. The preform must be exactly positioned relative to the apparatus so that all operations will be performed at the required position. Typical of these are locating metal preforms relative to numerical controlled precision machining devices, locating sheets of material relative to apparatus for punching patterns of holes in the sheets and positioning printed circuit boards relative to devices for installing very small parts very close together across the board surface.
Printed circuit boards normally have two tooling holes near one edge, with the distance between hole centerlines and hole diameters being exactly the same in a series of boards to be processed. The apparatus for performing operations on the boards, such as printing circuit patterns, punching holes for insertion of components, placing electronic components accurately relative to printed circuit patterns, etc. have two pins having diameters and spacing conforming to the tooling pin holes. The tooling pins are mounted on blocks to form tooling pin assemblies that can be fastened to a base, such as plates or rails at appropriate locations to support and align particular printed circuit boards.
In a typical printed circuit board printing process or component placement process, a series of identical boards are processed, then the apparatus is switched over to another series of different boards. While all boards in a series to undergo the same operation will have uniform pin spacing and diameter, boards in different series will generally have different spacing and diameter dimensions, since the boards will have different overall dimensions. In order to allow the apparatus to accommodate these different boards, the tooling pins are mounted on blocks or the like that can be removed from the apparatus and replaced with different blocks having different pin diameters and the replacement blocks will be secured to the apparatus at desired locations along a base or rails resulting in inaccurate positioning of components.
Because of the wide variety of tooling pin hole diameters used with different printed circuit boards, an inventory of a great number of precise, expensive, tooling pin assemblies must be maintained. While a machine is being set up for a particular series of boards, errors can be easily made in selecting tooling pin assemblies, resulting in pins too large or too small to exactly fit in the printed circuit board tooling holes. It is critical that the pins exactly fit the corresponding holes to assure accurate alignment. Where pins are too large, the board will not fit over them, with forcing resulting in damage to the board. If the pins are too small and the discrepancy is not noticed, succeeding boards will shift and not be positioned identically. Once the error in pin selection is noticed, the setup will need to be redone.
Where the printed circuit boards are manufactured in different batches, holes of different diameters may be used with different batches, requiring removal, replacement and realignment of the tooling pins between batches.
Attempt have been made to provide locator pins including means for assuring accurate engagement of tooling pins with printed circuit board tooling holes to accommodate slightly over size holes.
Typically of these is the apparatus described by Silverman in U.S. Pat. No. 4,244,109 in which one pin is cylindrical for engaging a cylindrical hole and the other is frusto-conical for engaging a tapered hole. As the tapered hole is forced over the conical pin, the board is forced toward the cylindrical pin. While this should assure contact with the cylindrical pin, the tapered hole is difficult to accurately manufacture and may be damaged as it is forced over the conical pin. Also, subsequent processing of the board on other devices having conventional cylindrical holes will not be possible.
Rich, in U.S. Pat. No. 3,957,371, describes a locating pin arrangement using one cylindrical pin and an expandable pin cooperating with two tooling hole in a printed circuit board. The expanding pin includes a tapered central shave and a segmented outer sleeve which expands when forced along the tapered core. This is a complex pin arrangement that can accommodate a slightly oversize hole but not holes of significant diameter difference. Rather than providing a way of using one pin assembly with holes of significantly varying diameters, the Rich assembly basically merely assures tight contact between pin and hole.
Therefore, there is a continuing need for locating pin assemblies for use with printed circuit boards and other preforms that utilize two spaced alignment holes that can accommodate significantly different diameter holes, is simple, reliable and inexpensive, does not require removal and replacement when different printed circuit boards or different series of boards having tooling holes of different diameters are to be processed and eliminates the necessity of providing a large inventory of tooling pin assemblies with a wide variety of tooling pin diameter.